"The vice-president says he was talking in general terms about a questioning program that is legal to save American lives, and he was not referring to water boarding," he said.

Evidence has emerged of the existence of secret CIA prisons

The BBC's Justin Webb in Washington DC asked whether it was possible that, 10 days before mid-term elections, the vice-president was signalling to hard-line Republicans that he preferred that the process was still being used.

The White House gave the impression that water boarding would be off limits when it pushed through a controversial terror bill just a few weeks ago, our correspondent says.

The US executive director of Amnesty International said Mr Cheney's gaffe revealed the US administration's true intentions for prisoner interrogation in the future.

"What's really a no-brainer is that no US official, much less a vice-president, should champion torture," said Larry Cox.

US interrogation techniques have been under the spotlight since evidence emerged of detainee abuse in Iraq and Afghanistan, and the existence of secret CIA prisons.